1. Field of the Invention
The present invention relates to both thermal mass transfer processes and thermal dye transfer imaging. In particular the present invention relates to the use of a first thermal mass transfer coating on a substrate to provide a background surface having a desirable appearance and which is receptive to a thermally transferred dye.
2. Background of the Invention
Thermal mass transfer and thermal dye transfer processes are technologies that bear some superficial similarities but which are distinct within the technical art. Both processes use a donor sheet and a receptor sheet. The thermal mass transfer donor sheet normally comprises a carrier layer with at least a thermally transferable colorant (a dye or preferably a pigment) in a heat softenable binder. The thermal dye transfer donor sheet comprises a carrier layer with at least a dye layer on the donor surface. The dye layer may consist of only dye or dye in a binder (the binder not transferring when the dye is thermally transferred). Both transfer sheets are used with the donor surface in intimate contact with a receptor material, and the donor sheet is heated in an imagewise manner (e.g., by thermal printheads, irradiation as by a laser or high intensity radiation transmitted through a mask or stencil) to transfer the image forming material. In the thermal mass transfer system, the donor layer is softened by the imagewise heating (and sometimes a receptor layer on the receptor sheet is contemporaneously softened), and the softened area is transferred to the receptor sheet. In thermal dye transfer, the dye is melted or vaporized to transfer to the receptor sheet and tends to be adsorbed and/or absorbed into the surface of the receptor element. The nature of the mechanism of adherence of the transferred image to the receptor sheet makes the nature of the surface of that receptor sheet important for each of the imaging processes. Surfaces which work well for receiving mass transfer images do not necessarily work well for thermal dye transfer.
It is also desirable in thermal dye transfer imaging to have greater image capability than conventional primary additive and subtractive colors. Thermal mass transfer has allowed for some use of more exotic colors and appearances by including fluorescent pigments and metallic pigments into the thermally transferred binders. There are no readily available metallic colors for use with dye transfer processes.
U.S. Pat. No. 4,472,479 (Hayes et al.) describes a light barrier fluorescent ribbon for impact printing which comprises a carrier layer, and on one surface of the carrier layer a binder layer of wax or polymeric resin and fluorescent dye, and a barrier pigment within that layer or in a separate layer. The barrier pigment is a finely divided pigment of reflective material (metal or metal appearing) which does not shift the wavelength of fluorescent light.
Japanese Published patent application (Kokai) 1-258,990 discloses a non-digital transfer donor sheets coated with heat meltable ink layer regions of 3 primary colors or 4 primary colors plus black and a region containing a fluorescent dye. Overprinting of the respective regions with fluorescent dye is disclosed. The dye image is formed by printing onto one sheet and then transferring the entire image.
Japanese Published patent application (Kokai) 63-281,890 discloses a recording material having a thermo-fusible ink layer containing a fluorescent compound and a thermo-fusible ink layer containing colorant and a thermo-fusible ink layer containing an extender with hiding power.
U.S. Pat. Nos. 4,627,997; 4,866,025; 4,871,714; 4,876,237; and 4,891,352. describe thermal transfer of various fluorescent materials. In preferred embodiments, the fluorescent materials are patch coated on a donor ribbon along with magenta, cyan and yellow ink patches. These patents are directed at colorless fluorescent inks that emit in the visible spectrum upon exposure to ultraviolet radiation.
U.S. Pat. No. 3,647,503 describes a multicolored heat transfer sheet in which colored layers are sequentially coated on a substrate. That patent is directed at multicolored transfer imaging and requires good porosity of the uppermost layer to provide good transfer of dye from lower layers.
WIPO published patent application number 10268 (1989) discloses a thermal transfer ribbon having a transfer coating including a fluorescent coloring material of a reddish-orange hue in a wax material. The transfer coating contains 50-90% wax, including 20-45% hydrocarbon wax, 35-65% paraffin wax, 2-30% carnauba wax and 2-25% acetate copolymer; 5-20% fluorescent pigment, and 5-20% color toning pigment.
The use of reflecting barrier pigments is also described in German Patent 3,042,526.
The present invention overcomes deficiencies of the prior art in providing good quality thermal dye transfer images that are generated by thermal transfer onto thermal mass transfer deposited backgrounds. The clarity and variety of thermal dye transfer images produced by this method is improved by thermal mass transferring an opaque white or metallic pigment layer prior to dye transfer.